The conventional technique to drive bobbin cores during a thread-winding operation involves providing a "knifed" or "serrated" drive head associated with the winder which physically digs into the bobbin core. The serrated drive head spins at high speeds and is intended to prevent the core from slipping during the thread-winding operation. In this regard, even small amounts of core slippage during thread-winding causes the bobbin to be out-of-specification due to incorrect thread tensions.
There are several disadvantages associated with the use of conventional serrated drive heads. Specifically, over time the serrations on the drive head become dull due to wear and tear. As they dull, small amounts of slippage may occur which is evidenced by incorrect thread tensions resulting in out-of-specification bobbins. In addition, small amounts of debris or other material may become trapped in the serrations which again might lead to relative slippage between the drive head and the bobbin core. Needless to say, the ends of the cores become scarred due to the frictional engagement with the serrated drive head--a possibility that can lead to structural weakness in the bobbin core and/or a core which becomes out-of-round.
The amount of spring pressure required to hold the drive heads against the bobbin core to prevent slippage can also cause operator difficulty during doffing of the wound bobbins and replacement with fresh bobbin cores. That is, as the serrated drive head becomes worn, greater spring pressures are needed in order to overcome the tendency of the bobbin core to slip.
Recently, novel magnetic bobbin cores and sideless pre-wound bobbins employing the same are disclosed in copending U.S. patent application Ser. No. 09/447,740 filed concurrently herewith, the entire content of which is expressly incorporated hereinto by reference. In general, such bobbin cores include a cylindrical core with at least one end thereof being permanently magnetized. In preferred forms, the bobbin cores are formed from a thermoplastic or thermoset resin in which magnetized particles are dispersed. The problems noted above, can sometimes be exacerbated by the permanent magnetism exhibited by such bobbin cores.
It would therefore be highly desirable if bobbin cores, especially magnetized bobbin cores, could be provided which overcome these difficulties. It is toward providing solutions to such problems that the present invention is directed.
Broadly, the present invention is embodied in cylindrical bobbin cores which have at least one radially oriented slot formed in at least one end thereof. The slot is sized and configured to mate with a radially extending blade associated with the drive head of the winder so as to achieve positive rotational drive therebetween. In view of this interconnection between the core and the drive head, significantly less spring pressure needs to be exerted against the core by the tail stock of the winder.
These, and other, aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.